2004 Buick Ranier. Oil gauge never returns to zero, even with ignition off it stays around 80. With engine running it pegs to max. Thought of first that it might be sending unit but I think that even with a bad sending unit the gauge should return to zero with ignition off. Now I'm thinking the gauge itself is bad. Yes or no?

 

I think you joined the wrong forum, but I would suspect that it is the gauge due to the fact that it doesn't drop when the key is off. The sending unit cant send any signal to the gauge with the key off, so that's out as a possibility.